When you are going to choose data types for your table be careful about it because it will directly impact your query performance.

that happens due to data pages memory limitation (DATA PAGES are fundamental unit of storage that have the actual data rows of any table).

Each page has  8KB size and if any table has exceeded it's size than again another 8KB will be assigned to that table to store rest of the data;

here jump between pages occurred while fetching the record from that table which is memory intensive.

For Example if you have to choose any numeric data type than it will be better to choose Integer rather than decimal (Here I am concentrating about memory

usage not the rage of that data type It will also be in consideration while choosing but here I am discussing about memory )

For the Details please follow : http://msdn.microsoft.com/en-us/library/ms190969.aspx

and don't forget to read the bottom of that web link IT HAVE 3 IMPORTANT POINTS